The Washington Auto Loan Calculator estimates your real monthly car payment in Washington, with the state’s 6.50% vehicle sales tax rolled into the amount you finance. Many payment calculators ignore sales tax, which understates what you actually borrow.
How it works
The tool builds your financed amount in three steps, then amortizes it.
- Trade-in credit — your trade-in value is subtracted from the car price first.
- Washington sales tax — Washington charges 6.50% on the price after the trade-in credit. The calculator multiplies the taxable amount by 1.065 to add the tax.
- Down payment — your cash down is subtracted to give the financed balance.
The monthly payment uses the standard amortization formula:
M = P * r * (1 + r)^n / ((1 + r)^n - 1)where P is the financed amount, r is the monthly rate (APR / 12), and n is the number of months (years * 12). When the APR is 0, the payment is simply P / n.
Example
Take a $32,000 car in Washington with a $6,000 trade-in and $3,000 down, financed at 7.5% APR over 5 years. Washington’s 6.50% sales tax on the $26,000 taxable amount adds about $1,690, bringing the taxed price to about $27,690. After the $3,000 down payment you finance about $24,690. That works out to roughly $494.74/month, with about $4,994 in total interest over the 5-year term.
Notes
This is an estimate for planning only, not financial or tax advice. The 6.50% figure is Washington’s statewide vehicle sales-tax rate; some counties or cities add local tax, and trade-in tax treatment can vary. Title, registration and dealer fees are not included. Verify the exact tax, fees and APR with your Washington dealer, lender and the Washington Department of Revenue or motor-vehicle agency before committing.